Fuel injection system with accumulator fill valve assembly

ABSTRACT

A fuel injection system ( 10 ) having an accumulator ( 24 ) includes an accumulator fill valve assembly ( 20 ) that regulates pressure within the accumulator ( 24 ) for operation of injection events other than the main injection. A restriction ( 128 ) in an inlet conduit and a stepped surface in a spool valve ( 112 ) provide a pressure amplifier across the accumulator valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority on International Application No.PCT/US03/36773, filed Nov. 14, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to pump systems for fuel injection systems.

2. Description of the Related Art

Engine exhaust emission regulations are becoming increasinglyrestrictive. One way to meet emission standards is to precisely controlthe quantity and timing of the fuel injected into the combustion chamberto match the engine cycle. For certain engine operating conditions,effective injection rate shaping may result in reduced levels ofparticulates and oxides of nitrogen in the engine exhaust. Such rateshaping may comprise multiple injection events including early pilot,close pilot and early and late post injection in addition to shaping themain injection event.

Some existing rate shaping techniques attempt to control injection ratesby making various modifications to the injector nozzle assembly. Anotherrate shaping technique utilizes a separate control valve to provide moreprecise rate shaping than with modified injector nozzle assemblies. Anexample of such a control valve is disclosed in U.S. Pat. No. 6,276,610to Spoolstra et al.

Fuel injection systems that utilize one or more control valves in unitpumps or unit injectors typically have cam driven pumps that providegood pressure capability, smooth beginning of injection characteristics,compact size and lower cost. However, among the disadvantages of unitpumps or unit injectors are design constraints imposed by the cam, andcomplexity in valve design and valve actuation.

Another rate shaping technique utilizes a common rail system wherehigh-pressure fuel is stored in a common rail and injection events arecontrolled by a single needle control valve in each injector. Commonrail systems are highly effective for multiple injection events, yetthey too have some disadvantages. Common rail systems typically have alarge number of high-pressure connections that increase opportunitiesfor leakage. Also, the distance between the rail and the injector nozzleresults in pressure waves that inhibit repeatable valve behavior.

One proposed solution is disclosed in DE 199 63 219 where an accumulatoris provided between the pump and the injector for each cylinder. Oneproblem with this solution, however, is that pressure in the accumulatoris still constrained by the design of the cam and no direct controls areprovided to regulate the pressure in the accumulator.

SUMMARY OF THE INVENTION

The foregoing problems are solved by the present invention of a fuelinjection system of the type having a pump system including a plunger ina pumping chamber, and an injector having a nozzle that can be openedand closed by a control valve wherein an injection event will occur whenthe control valve is actuated and will not occur when the control valveis not actuated. An accumulator is fluidly connected between the pumpsystem and the injector to store pressurized fuel for injection eventsindependent of the pump system. Typically, a fuel supply will providefuel to the pump system and to the injector by way of the accumulator.According to the invention, an accumulator fill valve assembly ismounted in fluid communication with the accumulator and is operablebetween an open condition and a closed condition. Thus, in the opencondition, the accumulator is in fluid communication with the pumpingchamber and in the closed condition, the accumulator is not in fluidcommunication with the pumping chamber.

Preferably, the accumulator fill valve assembly comprises a spool, oneportion of which is in fluid communication with the fuel supply, andanother portion of which is in fluid communication with the accumulator.When pressure in the accumulator exceeds a set point, the spool will bemoved against pressure in the fuel supply to the open condition.

In one aspect of the invention, pressure in the fuel supply isadjustable, and adjusting the fuel supply pressure will also adjust theset point. In another aspect of the invention the spool is biasedagainst pressure in the accumulator by a spring. Alternatively, thespool has a portion in fluid communication with the pumping chamberwherein pressure in the pumping chamber biases the spool againstpressure in the accumulator.

Preferably, the accumulator fill valve assembly has an inlet conduit influid communication with the pumping chamber and a restriction in theinlet conduit. The restriction establishes a pressure drop between thepumping chamber and accumulator. This pressure drop serves both to addto a pressure amplification between supply pressure and accumulatorpressure, as well as to assist in fill valve positioning with flowinduced forces. In this case, the accumulator valve further comprises astepped valve element. Also, preferably, the injector has a nozzleneedle control chamber, and a conduit extends between the accumulatorfill valve assembly and the nozzle needle control chamber.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a fuel injection system with anaccumulator fill valve assembly according to the invention in the closedposition.

FIG. 2 is a schematic diagram of a fuel injection system with anaccumulator fill valve assembly according to the invention in the openposition.

FIG. 3 is a schematic diagram of a fuel injection system with analternate embodiment of an accumulator fill valve assembly according tothe invention in the open position.

FIG. 4 is a schematic diagram of a fuel injection system with analternate embodiment of an accumulator fill valve assembly according tothe invention in the closed position.

FIG. 5 is a schematic diagram of a fuel injection system with a thirdembodiment of an accumulator fill valve assembly according to theinvention in the open position.

FIG. 6 is a schematic diagram of a fuel injection system with a thirdembodiment of an accumulator fill valve assembly according to theinvention in the closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fuel injection system incorporating the invention is generallyindicated schematically at 10, in FIGS. 1 and 2. A pump system 12includes an engine driven cam 14 that drives a plunger 16 in a pumpingchamber 18. The pumping chamber 18 is connected to an accumulator fillvalve assembly 20 via a high-pressure fluid line 22. The accumulatorfill valve assembly 20 is fluidly connected to an accumulator 24, whichin turn is fluidly connected to an injector 26. It will be understoodthat the pump system 12 may be a unit pump connected via a high-pressurefluid line to the injector 26, or alternatively, may be incorporatedinto a unit injector. Further, it is appreciated that there are manydifferent ways to implement the present invention in accordance with theschematic illustrations in FIGS. 1 and 2.

The injector 26 has a needle 28 that is biased to close spray holes 30in a nozzle 32 by a combination of a spring 34 and fluid pressure. Meansare provided to control injection events in the injector 26. Here, anozzle needle control valve 36 is disposed in fluid communication withthe top of the nozzle 32. The injector is fluidly connected to theaccumulator 20 by a high-pressure fuel line 38. Also, an inlet throttle39 upstream of the top of the nozzle 32 and fluidly connected to thehigh-pressure fuel line helps to control injection events, andespecially proper and timely closure of the needle 28.

A fuel injection event is triggered by actuating the nozzle needlecontrol valve 36, which normally occurs electronically. Actuation causesa pressure differential across the needle 28 that lifts the needle, andinitiates the injection event. It will be appreciated that other meansare known in the art to control injection events. The particular mannerof injection control is not critical to the invention.

Looking now more closely at the accumulator fill valve assembly 20 andthe accumulator 24, it can be seen that they are modular in that theyare directly mounted to each other with the accumulator 24 open to theaccumulator fill valve assembly 20. The accumulator fill valve assembly20 has an internal bore 40, which is open at one end to the accumulator24 and at the other end to a fuel supply conduit 42. The fuel supplyconduit 42 communicates with a fuel supply 43, and the nozzle needlecontrol valve 36 also communicates with the fuel supply 43 inconventional manner. A spool valve 44 reciprocates in the internal bore40. An inlet conduit 46 is in fluid communication with the high-pressurefluid line 22. A one-way check valve 47 prevents flow reversal in theinlet conduit 46. First and second connecting conduits 48, 50 fluidlyconnect the inlet conduit 46 to the internal bore 40. An accumulatorsupply conduit 52 has at least a portion coaxial with the secondconnecting conduit 50, and extends between the internal bore 40,opposite the second connecting conduit 50, and the accumulator 24. Afuel supply connecting conduit 54 has at least a portion thereofslightly offset from the axis of the first connecting conduit 48, andextends between the internal bore 40, opposite the first connectingconduit 48, and the fuel supply conduit 42.

The spool valve 44 has a first transverse passage 56 and a secondtransverse passage 58. The first transverse passage 56 is disposed toestablish communication between the first connecting conduit 48 and thefuel supply connecting conduit 54. The second transverse passage 58 isdisposed to establish fluid communication between the second connectingconduit 50 and the accumulator supply conduit 52. The passages 56, 58are disposed so that when one establishes communication, the other willnot. A spring 60 biases the spool valve 44 so that one end 62 thereof isurged toward the accumulator 24. An antilock orifice 64 extends betweenthe first transverse passage 56 and the other end 66, which is in fluidcommunication with the fuel supply conduit 42. The antilock orifice 64is intended to avoid a hydraulic lock of the spool valve 44.

It will be apparent that the position of the spool valve 44 in theinternal bore 40 depends upon the force of the spring 60, the pressurein the fuel supply conduit 42, the pressure in the pumping chamber 18(as communicated to the high-pressure fluid line 22, the inlet conduit46 and the first and second connecting conduits 48, 50), and thepressure in the accumulator 24. The cross-sectional area of the one end62 determines the force exerted on the spool valve 44 by pressure in theaccumulator 24. The force is counteracted by the force of the spring 60and pressure in the fuel supply conduit 42. A set point of accumulatorpressure can thus be adjusted by controlling fuel supply pressure. Fuelsupply pressure is controlled by pressure regulator 45, which in aconventional manner would comprise a fuel pressure circuit, controlvalve, or other pressure regulation means.

The accumulator fill valve assembly 20 is illustrated in the closedposition in FIG. 1 and in the open position in FIG. 2. In the closedposition, the transverse passage 56 establishes fluid communicationbetween the first connecting conduit 48 and the fuel supply connectingconduit 54. Meanwhile, fluid communication between the second connectingconduit 50 and the accumulator conduit 52 is blocked. In the openposition, the transverse passage 58 establishes fluid communicationbetween the second connecting conduit 50 and the accumulator conduit 52.Meanwhile, fluid communication between the first connecting conduit 48and the fuel supply pressure conduit 54 and the fuel supply line 42 isblocked.

At the beginning of an injection cycle, the accumulator fill valveassembly 20 will normally be open because pressure in the accumulator 24will normally be below the set point. As the cam 14 rotates and theplunger 16 moves, fuel is pumped into the high-pressure fluid line 22,the inlet conduit 46, the second connecting conduit 50, the secondtransverse passage 58, the accumulator connecting conduit 52 to theaccumulator 24 and the high-pressure fuel line 38. Because the injector26 is closed, pressure builds in the accumulator 24 until it reaches theset point. When the accumulator set point is reached, the force exertedon the spool valve 44 overcomes the counteracting forces of the spring60 and the pressure in fuel supply line 42, and the accumulator fillvalve assembly 20 closes to the position shown in FIG. 1.

When the nozzle needle control valve 36 initiates main injection, fuelis released from the accumulator 24 and high-pressure line 38 throughthe nozzle 32. As pressure in the accumulator 24 drops below the setpoint, the accumulator fill valve assembly 20 reopens, establishingdirect fluid communication between the pumping chamber 18 and theinjector nozzle 32. In this mode, injection proceeds in a conventionalmanner.

When injection is terminated by deactivating the nozzle needle controlvalve 36, pressure again builds in the accumulator 24 (so long as theplunger 16 is still advancing into the pumping chamber 18) until itexceeds the accumulator set point and closes the accumulator fill valveassembly 20. At this point, the stored fuel in the accumulator 24 isavailable at high-pressure for auxiliary injection events other thanmain injection. Importantly, these injection events can occurindependently of the position of the cam 14 because the accumulator 24is cut off from fluid communication with the pumping chamber 18.Activating and deactivating the nozzle needle control valve 36 can thenaccomplish control of auxiliary injection events.

For example, a post injection event is triggered by actuating the nozzleneedle control valve 36, which opens the nozzle 32 and releases fuelfrom the accumulator 24, independent of the position of the cam 14.Simply closing the nozzle needle control valve 36 ends the postinjection event. Moreover, control of injection pressure during anyinjection event can be achieved by adjusting the fuel supply pressure,thereby adjusting the accumulator set point of the accumulator 24. Forexample, if injection pressure is desired to be lower as in a light loadengine operation, a pressure regulator valve in the engine's fuel supplycircuit can lower the fuel supply pressure, thereby lowering theaccumulator set point above which the accumulator fill valve assembly 24will close.

FIGS. 3 and 4 illustrate an alternative embodiment 10′ of a fuelinjection system with an accumulator valve according to the inventionthat obviates any need for springs or a check valve. In the embodimentof FIGS. 3 and 4, components common to the embodiment of FIGS. 1 and 2bear like reference numerals. An accumulator fill valve assembly 100 hasa body comprising stepped internal bore 102 with a larger diameterportion 104, a smaller diameter portion 106 and a load portion 108. Onestep is defined by a shoulder 110 between the larger diameter portion104 and the smaller diameter portion 106. The larger diameter portion104 communicates with the fuel supply conduit 42. The load portion 108extends from the larger diameter portion 104 to communicate with thehigh-pressure fluid line 22 via load line 109.

A spool valve 112 comprise a medial spool 114 that reciprocates withinthe larger diameter portion 104 of the internal bore, a pressure pin 116that extends into the smaller diameter portion 106, and a load pin 118that extends into the load portion 108. A first transverse passage 120in the spool 112 (here in the medial spool 114) is disposed to establishcommunication between the first connecting conduit 48 and the fuelsupply connecting conduit 54. A second transverse passage 122 in thespool 112 (here in the pressure pin 116) is disposed to establish fluidcommunication between the second connecting conduit 50 and theaccumulator supply conduit 52. The passages 120, 122 are disposed sothat when one establishes communication, the other will not.

An antilock orifice 124 extends between the first transverse passage 120and one end 126 of the medial spool 114, which is in fluid communicationwith the fuel supply conduit 42. The antilock orifice 124 is intended toavoid a hydraulic lock of the spool valve 112. A step surface 127 at theother end of the medial spool 114 abuts the shoulder 110 when theaccumulator 24 is below the set point. The shoulder 110 is vented (notshown) to permit the medial spool 114 to reciprocate without drawing avacuum in the larger diameter portion 104 between the step surface 127and the shoulder 110.

A restriction 128 is disposed in the inlet conduit 46 between thehigh-pressure fluid line 22 and the first connecting conduit 48.Operation of the accumulator fill valve assembly 100 is the same asexplained above with respect to the embodiment of FIGS. 1 and 2, exceptthat the restriction 128, along with the pressure on the spool 112 andthe load pin 118, creates a pressure drop that achieves a self-enhancingpressure amplification across the accumulator fill valve assembly. Theamplification ratio is determined by the relative sizes of the pressurepin 116, the medial spool 114 and the load pin 118. In this case,pressure in the accumulator 24 acts on the pressure pin 116 to generatea force that is counteracted by the pressure in the high pressure loadline 109 acting on the load pin 118 plus the pressure of the fuel supplyacting on the end 126 of the medial spool 114. The size of therestriction 128 need only be sufficient to create a pressuredifferential large enough to move the mass of the spool valve 112.Preferably, there will be a high amplification ratio from the fuelsupply side of the spool valve 112 to the accumulator side.

It is appreciated that upon opening the nozzle needle control valve 36to commence main injection, for example, a sudden pressure drop in theaccumulator 24 due to the open nozzle 32 may cause the nozzle toreclose, partially or fully, while pressure is building up in theaccumulator 24. An undesirable “dip” in the rate of injection wouldresult In order to ensure that the accumulator fill valve assembly willpreemptively open only when the nozzle needle control valve 36 isactuated and when the plunger 16 is advancing, the embodiment of FIGS. 5and 6 provides an alternate accumulator fill valve assembly 200 that isidentical in every respect to that of FIGS. 3 and 4, except that apressure conduit 202 extends between the top of the nozzle 32 and theshoulder 110. Thus, pressurized fuel in the pressure conduit 202 willgenerate a force on the step surface 127 of the medial spool 114. Here,when the nozzle needle control valve 36 is closed, pressure in theaccumulator 24 acts on the pressure pin 116 and also on the step surface127 so that the accumulator fill valve assembly 200 will remain openuntil the accumulator pressure reaches the accumulator set point. InFIG. 6, the accumulator fill valve assembly 200 is closed and willremain closed as long as the nozzle needle control valve 36 is notactuated because the accumulator pressure exceeds the accumulator setpoint. But when the nozzle needle control valve 36 is actuated, theaccumulator fill valve assembly 200 will open quickly and remain open aslong as the plunger 16 is advancing while the nozzle needle controlvalve 36 is actuated.

While the invention has been specifically described in connection withcertain specific embodiments thereof, it is to be understood that thisis by way of illustration and not of limitation, and the scope of theappended claims should be construed as broadly as the prior art willpermit.

1. A unit fuel injector comprising: a pump including a plunger in apumping chamber; a nozzle that can be opened and closed by a controlvalve, wherein an injection event will occur when the control valve isactuated and will not occur when the control valve is not actuated; anaccumulator fluidly connected between the pump and the nozzle to storepressurized fuel at high pressure for injection events independent ofthe pump; a fuel supply for supplying fuel to the pump and to the nozzleby way of the accumulator; and an accumulator fill valve assemblymounted between the pump and the nozzle in high pressure fluidcommunication with the accumulator and operable between an opencondition and a closed condition, wherein the accumulator fill valveassembly comprises a spool, one portion of which is in fluidcommunication with the fuel supply, and another portion of which is influid communication with the accumulator, whereby in the open condition,the accumulator is in fluid communication with the pumping chamber andin the closed condition, the accumulator is not in fluid communicationwith the pumping chamber and when pressure in the accumulator exceeds aset point the spool will be moved against pressure in the fuel supply tothe closed condition.
 2. A unit fuel injector according to claim 1wherein pressure in the fuel supply is adjustable and adjusting the fuelsupply pressure will adjust a set point, above which the accumulatorfill valve assembly will close.
 3. A unit fuel injector according toclaim 1 wherein the spool is biased against pressure in the accumulatorby a spring.
 4. A unit fuel injector according to claim 1 wherein thespool has a portion in fluid communication with the pumping chamber andwherein pressure in the pumping chamber biases the spool againstpressure in the accumulator.
 5. A unit fuel injector according to claim1 where the spool has different diameters to establish an amplificationratio across the accumulator fill valve assembly.
 6. A unit fuelinjector comprising: a pump including a plunger in a pumping chamber; anozzle that can be opened and closed by a control valve, wherein aninjection event will occur when the control valve is actuated and willnot occur when the control valve is not actuated; an accumulator fluidlyconnected between the pump and the nozzle to store pressurize fuel athigh pressure for injection events independent of the pump; a fuelsupply for supplying fuel to the pump and to the nozzle by way of theaccumulator; and an accumulator fill valve assembly mounted between thepump and the nozzle in high pressure fluid communication with theaccumulator and operable between an open condition and a closedcondition, wherein the accumulator fill valve assembly has an inletconduit in fluid communication with the pumping chamber and arestriction in the inlet conduit to establish a self enhanced pressureamplifier across the accumulator valve.
 7. A unit fuel injectoraccording to claim 6 further comprising a stepped valve element.
 8. Aunit fuel injector according to claim 6 further comprising a conduitextending between the accumulator fill valve assembly and the top of thenozzle.
 9. A unit fuel injector according to claim 2 wherein the spoolis biased against pressure in the accumulator by a spring.
 10. A unitfuel injector according to claim 2 wherein the spool has a portion influid communication with the pumping chamber and wherein pressure in thepumping chamber biases the spool against pressure in the accumulator.11. A unit fuel injector according to claim 2 where the spool hasdifferent diameters to establish an amplification ratio across theaccumulator fill valve assembly.
 12. A unit fuel injector according toclaim 3 where the spool has different diameters to establish anamplification ratio across the accumulator fill valve assembly.
 13. Aunit fuel injector according to claim 4 where the spool has differentdiameters to establish an amplification ratio across the accumulatorfill valve assembly.
 14. A unit fuel injector according to claim 1wherein the accumulator fill valve assembly has an inlet conduit influid communication with the pumping chamber and a restriction in theinlet conduit to establish a self enhanced pressure amplifier across theaccumulator valve.
 15. A unit fuel injector according to claim 2 whereinthe accumulator fill valve assembly has an inlet conduit in fluidcommunication with the pumping chamber and a restriction in the inletconduit to establish a self enhanced pressure amplifier across theaccumulator valve.
 16. A unit fuel injector according to claim 3 whereinthe accumulator fill valve assembly has an inlet conduit in fluidcommunication with the pumping chamber and a restriction in the inletconduit to establish a self enhanced pressure amplifier across theaccumulator valve.
 17. A unit fuel injector according to claim 1 furthercomprising a conduit extending between the accumulator fill valveassembly and the top of the nozzle.
 18. A unit fuel injector accordingto claim 2 further comprising a conduit extending between theaccumulator fill valve assembly and the top of the nozzle.
 19. A unitfuel injector according to claim 3 further comprising a conduitextending between the accumulator fill valve assembly and the top of thenozzle.
 20. A fuel injection system comprising: a pump system includinga plunger in a pumping chamber; an injector having a nozzle that can beopened and closed by a control valve, wherein an injection event willoccur when the control valve is actuated and will not occur when thecontrol valve is not actuated; an accumulator fluidly connected betweenthe pump system and the injector to store pressurized fuel at highpressure for injection events independent of the pump system; and a fuelsupply for supplying fuel to the pump system and to the injector by wayof the accumulator; characterized by: an accumulator fill valve assemblymounted between the pump system and the injector in high pressure fluidcommunication with the accumulator and operable between an opencondition and a closed condition, wherein the accumulator fill valveassembly comprises a spool, one portion of which is in fluidcommunication with the fuel supply, and another portion of which is influid communication with the accumulator, and the accumulator fill valveassembly has an inlet conduit in fluid communication with the pumpingchamber and a restriction in the inlet conduit to establish a selfenhanced pressure amplifier across the accumulator valve, whereby in theopen condition, the accumulator is in fluid communication with thepumping chamber and in the closed condition, the accumulator is not influid communication with the pumping chamber and when pressure in theaccumulator exceeds a set point the spool will be moved against pressurein the fuel supply to the closed condition.
 21. A fuel injection systemcomprising: a pump system including a plunger in a pumping chamber; aninjector having a nozzle that can be opened and closed by a controlvalve, wherein an injection event will occur when the control valve isactuated and will not occur when the control valve is not actuated; anaccumulator fluidly connected between the pump system and the injectorto store pressurized fuel at high pressure for injection eventsindependent of the pump system; and a fuel supply for supplying fuel tothe pump system and to the injector by way of the accumulator;characterized by: an accumulator fill valve assembly mounted between thepump system and the injector in high pressure fluid communication withthe accumulator and operable between an open condition and a closedcondition, wherein the accumulator fill valve assembly comprises aspool, one portion of which is in fluid communication with the fuelsupply, and another portion of which is in fluid communication with theaccumulator, whereby in the open condition, the accumulator is in fluidcommunication with the pumping chamber and in the closed condition, theaccumulator is not in fluid communication with the pumping chamber. 22.A fuel injection system comprising: a pump system including a plunger ina pumping chamber; an injector having a nozzle that can be opened andclosed by a control valve, wherein an injection event will occur whenthe control valve is actuated and will not occur when the control valveis not actuated; an accumulator fluidly connected between the pumpsystem and the injector to store pressurized fuel at high pressure forinjection events independent of the pump system; and a fuel supply forsupplying fuel to the pump system and to the injector by way of theaccumulator; characterized by: an accumulator fill valve assemblymounted between the pump system and the injector in high pressure fluidcommunication with the accumulator and operable between an opencondition and a closed condition, wherein the accumulator fill valveassembly comprises a spool, one portion of which is in fluidcommunication with the fuel supply, and another portion of which is influid communication with the accumulator, and further comprising aconduit extending between the accumulator fill valve assembly and thetop of the nozzle, whereby in the open condition, the accumulator is influid communication with the pumping chamber and in the closedcondition, the accumulator is not in fluid communication with thepumping chamber.